Vanadate-Induced Inhibition of BCR-Triggered Apoptosis is Coupled with Tyrosine Phosphorylation and Induction of G2M Growth Arrest in Ramos-BL B Cells

Abstract

The regulation of the tyrosine phosphorylation of key signaling molecules by tyrosine kinases and phosphatases is essential for BCR-triggered signaling cascades during B cell selection process. We used the non-selective tyrosine phosphatase inhibitor vanadate to study the importance of the late regulation of the tyrosine phosphorylation for BCR-triggered G1 growth arrest and apoptosis in Ramos-BL B cells. Vanadate induces G2M growth arrest in a dose-dependent manner and prevents BCR-triggered apoptosis. Vanadate-induced upregulation of the tyrosine phosphorylation is concomitant with increased expression of cyclin B and inhibition of caspase-3 activation and PARP cleavage. The anti-apoptotic effect of vanadate was observed even when added up to 6 hours after the treatment of Ramos-BL B cells with anti-IgM. Vanadate increases BCR-triggered tyrosine phosphorylation of the cytosolic tyrosine phosphatases, SHP-1 and SHP-2 after 24 hours. Co-stimulation with anti-CD40 prevents anti-IgM-triggered tyrosine phosphorylation of these phosphatases and up-regulates the expression of SHP-1. We conclude that the regulation of the tyrosine phosphatase activity is indispensable for BCR-triggered execution of the apoptosis in Ramos-BL B cells.

Keywords:

• B lymphocytes
• tyrosine phosphorylation
• antigen receptor
• CD40
• vanadate
• apoptosis
• SHP-1
• SHP-2

ABBREVIATIONS
BCR:	=	B cell antigen receptor;
BL:	=	Burkitt's lymphoma;
EBV:	=	Epstein-Barr virus;
PI:	=	propidium iodide;
PTK:	=	protein tyrosine kinase(s);
PTP:	=	protein tyrosine phosphatase(s);
ROS:	=	reactive oxygen species.